Recently, high voltage electrical storage devices in which a charge voltage and a discharge voltage of a single electrical storage element each exceeds 1.5 V have been progressively developed. As such high voltage electrical storage devices, lithium primary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, electric double layer capacitors and the like have been put into practice.
For a high voltage electrical storage device, a nonaqueous electrolytic solution using an organic compound as a solvent is used. The reason for this is that water, if used as the solvent of the electrolytic solution, is electrolyzed by the high charge voltage and discharge voltage. A nonaqueous electrolytic solution is also used for an electrical storage device including an electrode which contains active lithium reactive with water and uses occlusion or release of lithium.
The nonaqueous electrolytic solution is desired to have a high conductivity and a low viscosity in order to improve the discharge performance of the electrical storage device in which the nonaqueous electrolytic solution is used. When used as a solvent for a secondary battery, an electric double layer capacitor or the like, the nonaqueous electrolytic solution needs to be stable chemically and electrochemically in order not to deteriorate the performance of the electrical storage device as a result of the repetition of charge/discharge cycles.
From these points of view, for example, as a main solvent of the electrolytic solution of a lithium ion secondary battery, a mixed system of a cyclic carbonate (cyclic carbonic acid ester) represented by ethylene carbonate and a chain carbonate (chain carbonic acid ester) represented by ethylmethyl carbonate or dimethyl carbonate is conventionally used. As a main solvent of the electrolytic solution of an electric double layer capacitor, a cyclic carbonate represented by propylene carbonate is preferably used.
The above-described electrical storage devices are widely used as a main power source, a backup power source or an electric circuit power source for mobile communication devices or portable electronic devices. Such mobile and portable devices are recently desired to be more compact and to have higher performance. Thus, the electrical storage devices are required to be further improved in the volumetric energy density.
In order to improve the volumetric energy density, it is necessary to improve the average discharge voltage and the volumetric capacitance density. As one measure for realizing this, it is proposed to increase the charge voltage.
In the case of a lithium ion secondary battery, the utilization factor of lithium as a positive electrode material can be improved by raising the charge voltage. As a result, the volumetric capacitance density is increased. As the positive electrode material, a lithium-containing transition metal oxide such as lithium cobalt oxide, lithium nickel oxide or the like is generally used. In the case of an electric double layer capacitor, the value of the electric double layer capacitance can be increased by raising the charge voltage. As a result, the volumetric capacitance density can be increased.
However, in the case where one of a pair of electrodes is charged to a level equal to or higher than 4.3V on the basis of the dissolution/deposition potential of lithium, the following occurs. Even when a conventional chain carbonate or cyclic carbonate which is known to be superb in oxidation resistance and so usable as a nonaqueous solvent suitable to a high voltage electrical storage device is used, such a carbonate is oxidized and decomposed to generate gas. Such a decomposition reaction conspicuously proceeds especially in a high temperature state and is accompanied by generation of a large amount of gas. Therefore, for example, where an internal-pressure-sensitive current interrupt device (CID) for blocking the charging current against excessive charge of a battery is mounted on a high voltage lithium ion secondary battery containing such a nonaqueous solvent, the CID may malfunction to cause the lithium ion secondary battery to lose the function as a battery. In the case where the CID is not mounted, a problem arises that when the amount of gas generation is excessive, the battery is swelled.
Patent Document 1 discloses a nonaqueous electrolytic secondary battery using a nonaqueous electrolytic solution containing cyclic sulfonic acid ester in order to suppress the chain carbonate or the cyclic carbonate from being oxidized and decomposed at a super high potential. In such a nonaqueous electrolytic secondary battery, when the positive electrode is charged to a potential equal to or higher than 4.5V, the cyclic sulfonic acid ester is oxidized and decomposed on the positive electrode side, and a surface of the positive electrode is covered with a film. This film suppresses the solvent from being decomposed on the surface of the positive electrode.
Patent Documents 2 and 3 propose incorporating, into a nonaqueous solvent, a “hydrocarbon compound which may contain a fluorine atom” at 0.01% by volume or greater and 5% by volume or less. These patent documents describe that because a hydrocarbon compound which is stable against oxidation and reduction is present at an activation point on the surface of the electrode, sub reaction of the electrolytic solution component and the electrode active material can be suppressed in a high temperature state.